A fuel cell is a device that converts the chemical energy of fuels directly to electrical energy and heat. In its simplest form, a fuel cell comprises two electrodes—an anode and a cathode—separated by an electrolyte. During operation, a gas distribution system supplies the anode and the cathode with fuel and oxidizer, respectively. Typically, fuel cells use the oxygen in the air as the oxidizer and hydrogen gas (including hydrogen produced by reforming hydrocarbons) as the fuel. Other viable fuels include reformulated gasoline, methanol, ethanol, and compressed natural gas, among others. For polymer electrolyte membrane (‘PEM’) fuel cells, each of these fuels must be reformed into hydrogen fuel. However, in direct methanol fuel cells, methanol itself is the fuel. The fuel undergoes oxidation at the anode, producing protons and electrons. The protons diffuse through the electrolyte to the cathode where they combine with oxygen and the electrons to produce water and heat. Because the electrolyte acts as a barrier to electron flow, the electrons travel from the anode to the cathode via an external circuit containing a motor or other electrical load that consumes power generated by the fuel cell.
A complete fuel cell generally includes a pair of separator plates or plate assemblies on either side of the electrolyte. A conductive backing layer may also be provided between each plate and the electrolyte to allow electrons to move freely into and out of the electrode layers. Besides providing mechanical support, the plate assemblies define fluid flow paths within the fuel cell, and collect current generated by oxidation and reduction of the chemical reactants. The plate assemblies are gas-impermeable and have channels or grooves formed on one or both surfaces facing the electrolyte. The channels distribute fluids (gases and liquids) entering and leaving the fuel cell, including fuel, oxidizer, water, and any coolants or heat transfer liquids. Each plate assembly may also have one or more apertures extending through the plate that distribute fuel, oxidizer, water, coolant and any other fluids throughout a series of fuel cells. Each plate assembly is made of an electron conducting material, including graphite, aluminum, other metals, and composite materials such as graphite particles imbedded in a thermosetting or thermoplastic polymer matrix. To increase their energy delivery capability, fuel cells are typically provided in a stacked arrangement of pairs of separator plates or plate assemblies with electrolyte between each plate pair or plate assembly pair. In this arrangement, one side of the plate assembly will be positioned adjacent to and interface with the anode of one fuel cell while the other side of the plate assembly will be positioned adjacent to and interface with the cathode of another fuel cell. Thus, the separator plate assemblies are referred to as ‘bipolar.’
Typical bipolar plate assemblies include an anode plate and a cathode plate bonded together using a conductive adhesive. As indicated above, coolant channels are typically formed by the assembly process, due to grooves on one plate mating with a flat surface or matching grooves on the other plate. As bipolar plate assemblies are driven to be thinner (<1 mm), the strength of the plate decreases. The apertures mentioned above define manifold holes for supply of reactants and product removal. These areas are particularly vulnerable to cracks. Thus, there is a need for a stronger bipolar plate assembly without significantly increasing the thickness of the assembly.